Method for treating bauxite waste

Abstract

To provide a bauxite waste treatment method that allows removal of CO2 with improved energy efficiency and makes it possible to recover rare metals.SOLUTION: A bauxite waste treatment method comprises: (a) a step of mixing red mud containing an alkaline component and a rare metal component with water to obtain an alkaline aqueous solution containing the alkaline component; (b) a step of bringing the alkaline aqueous solution into contact with a gas containing CO2 to obtain a carbonate aqueous solution; and (c) a step of recovering the rare metal component from the carbonate aqueous solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating bauxite waste. [Background technology]

[0002] Bauxite ore is commonly used as a raw material in the alumina smelting process. During this process, bauxite waste (commonly known as "red mud") is generated as a by-product during alumina extraction. Red mud is a mixture of sodium hydroxide solution with a high pH and metal oxides containing a wide variety of elements, and its treatment and management have been a long-standing challenge. Red mud contains toxic heavy metals and is highly alkaline, posing a risk of soil and water pollution. However, a suitable utilization method for red mud has yet to be found, and large amounts of it left behind could pose a potential risk to the environment and human health. One approach to reducing the volume of red mud processed is drying. This method aims to thoroughly remove water and reduce the volume of red mud by drying. However, this method does not solve the problem of red mud's final disposal; it merely reduces the amount of waste.

[0003] Patent Document 1 considers the simultaneous conservation of the environment and disposal of waste by reacting alkaline components in red mud with CO2 in a solvent such as methanol to precipitate and remove carbonates.

[0004] Furthermore, red mud contains rare metal components such as gallium, scandium, and vanadium in addition to common metal oxides such as iron, aluminum, titanium, and silicon, and these rare metal components are highly valuable as useful resources. In order to effectively utilize the rare metal components, Patent Document 2 considers concentrating the metals, rare metals, and rare earth metals present in red mud, converting them into a single product, and reusing it in the Bayer process. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2014-518762 [Patent Document 2] Special Publication No. 2019-529721 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional methods use organic solvents such as methanol to treat the alkaline components in red mud, but this is undesirable because it requires energy to treat the contaminated organic solvent, and is also undesirable because it requires a large amount of energy to concentrate the metal components in the red mud when recovering rare metals from the red mud.

[0007] Therefore, one aspect of the present invention aims to provide a bauxite waste treatment method that can remove CO2 while improving energy efficiency and recover rare metals. [Means for solving the problem]

[0008] The present invention includes, for example, the following inventions [1] to [8]. [1] (a) mixing red mud containing an alkaline component and a rare metal component with water to obtain an alkaline aqueous solution containing the alkaline component; (b) contacting the alkaline aqueous solution with a gas containing CO2 to obtain an aqueous carbonate solution; (c) recovering the rare metal component from the carbonate aqueous solution; A method for treating bauxite waste, comprising: [2] The bauxite waste treatment method according to [1], further comprising a solid-liquid separation step between the step (a) and the step (b) for removing solid components derived from the red mud. [3] The method for treating bauxite waste according to [1] or [2], wherein the gas is atmospheric air. [4] The method for treating bauxite waste according to any one of [1] to [3], wherein the step (b) comprises spraying the alkaline aqueous solution and contacting the alkaline aqueous solution with the gas. [5] The method for treating bauxite waste according to any one of [1] to [4], wherein the step (b) comprises contacting the alkaline aqueous solution with the gas by bubbling the gas in the alkaline aqueous solution. [6] The bauxite waste treatment method according to any one of [1] to [5], further comprising a solid-liquid separation step between the step (b) and the step (c) for removing at least one of solid components derived from the red mud and a portion of the carbonates. [7] The method for treating bauxite waste according to any one of [1] to [6], further comprising a membrane separation step between the step (b) and the step (c) for removing water from the aqueous carbonate solution. [8] The bauxite waste treatment method according to any one of [1] to [7], further comprising a step of releasing the carbonate aqueous solution from which the rare metal components have been recovered into the environment after the step (c). [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide a bauxite waste treatment method that can remove CO2 while improving energy efficiency and recover rare metals. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a configuration diagram showing an embodiment of a bauxite waste treatment facility according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or corresponding parts will be designated by the same reference numerals, and duplicated explanations will be omitted.

[0012] [Bauxite waste treatment facility] Fig. 1 is a block diagram showing one embodiment of a bauxite waste treatment facility according to the present invention. The bauxite waste treatment facility 100 shown in Fig. 1 includes a first solid-liquid separation device 11, a CO2 absorption device 12, a second solid-liquid separation device 13, a membrane separation device 14, a rare metal recovery device 15, and a storage tank 16.

[0013] Bauxite waste (red mud) generated during the extraction of aluminum oxide from bauxite is mixed with water to form a slurry. Red mud is a mixture of metal oxides, such as iron oxide (Fe2O3), aluminum oxide, silicon oxide, titanium oxide, calcium oxide, magnesium oxide, sodium oxide, and potassium oxide, and metal hydroxides, such as aluminum hydroxide, sodium hydroxide, calcium hydroxide, and magnesium hydroxide. Mixing the red mud with water extracts the alkaline components contained in the red mud. The extracted alkaline component is an alkaline aqueous solution, which is mixed with the solid components contained in the red mud to form a slurry. The slurry contains water, sodium aluminum dioxide, sodium tetrahydroxide aluminate, sodium hydroxide, calcium hydroxide, magnesium hydroxide, potassium hydroxide, scandium compounds, gallium compounds, and the like.

[0014] Conventionally, bauxite waste treatment involves mixing red mud with water to form a slurry, and then concentrating the slurry by drying or other methods to reduce the amount of slurry to be treated. In contrast, in the present invention, red mud is mixed with a sufficient amount of water, and the alkaline components contained in the red mud are extracted with water to obtain an alkaline aqueous solution (slurry) containing the alkaline components. The alkaline aqueous solution is then subjected to solid-liquid separation without concentration. Therefore, the bauxite waste treatment method of the present invention is more energy efficient than conventional methods.

[0015] A guideline for the amount of red mud and water to be mixed is, for example, an amount such that the amount of sodium hydroxide in the slurry is 5% by mass or less, based on the total mass of the slurry. The amount of sodium hydroxide in the slurry may be 3% by mass or less, 2% by mass or less, or 1% by mass or less, based on the total mass of the slurry. The amount of sodium aluminum dioxide in the slurry may be 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on the total mass of the slurry. The total amount of hydroxides other than sodium hydroxide (e.g., calcium hydroxide) in the slurry may be 3% by mass or less, 1% by mass or less, or 0.5% by mass or less, based on the total mass of the slurry. The total amount of rare metal components (e.g., scandium compounds, gallium compounds) in the slurry may be 1% by mass or less, 0.5% by mass or less, or 0.3% by mass or less, based on the total mass of the slurry. The red mud and water are mixed, for example, so that 200 parts by mass or more, 500 parts by mass or more, or 1000 parts by mass or more of water is mixed with 100 parts by mass of red mud.

[0016] In the first solid-liquid separator 11, the slurry (a mixture of solid components in red mud and an alkaline aqueous solution) transferred through the transfer pipe L11 is separated into solid and liquid. After the slurry has been separated into solid and liquid, the liquid component (alkaline aqueous solution) is transferred to the CO2 absorber 12 through the transfer pipe L12. After the slurry has been separated into solid and liquid, the solid component is discharged from the first solid-liquid separator 11 through the transfer pipe L13 and is rendered harmless. The first solid-liquid separator 11 may be, for example, a sedimentation thickener or other such device.

[0017] The alkaline aqueous solution transferred through the transfer pipe L12 contains water, sodium aluminum dioxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, potassium hydroxide, a scandium compound, a gallium compound, etc. The alkaline aqueous solution transferred through the transfer pipe L12 has a composition, for example, of 3 mass % sodium aluminum dioxide, 1 mass % sodium hydroxide, 0.1 mass % calcium hydroxide, 0.1 mass % magnesium hydroxide, 0.01 mass % potassium hydroxide, 0.1 mass % scandium compound, 0.2 mass % gallium compound, and the remainder being water.

[0018] The pH of the alkaline aqueous solution is greater than 7, and may be 9 or greater, 10 or greater, or 11 or greater.

[0019] The solid components discharged through the transfer pipe L13 are a mixture containing iron oxide (Fe2O3), aluminum oxide, aluminum hydroxide, silicon oxide, titanium oxide, etc. These solid components may be separated into individual components and used as raw materials for cement, roads, building materials, etc., or may be disposed of by landfill.

[0020] In the CO2 absorbing device 12, the alkaline aqueous solution transferred through the transfer pipe L12 comes into contact with the CO2-containing gas transferred through the transfer pipe L14. In the CO2 absorbing device 12, the contact between the alkaline aqueous solution and the CO2-containing gas causes the CO2 in the gas to react with the alkaline component in the alkaline aqueous solution, producing carbonate, which becomes a carbonate aqueous solution. Furthermore, the absorption of CO2 in the gas reduces the CO2 concentration in the gas. The CO2-containing gas may be atmospheric air or flue gas.

[0021] The CO2 concentration in the gas transferred through the transfer pipe L14 may be, for example, 1000 ppm or less, 700 ppm or less, or 500 ppm or less, or 100 ppm or more, 200 ppm or more, or 300 ppm or more.

[0022] The method for contacting the alkaline aqueous solution with the CO2-containing gas is not particularly limited, and is preferably a method that provides excellent contact efficiency between the alkaline aqueous solution and the CO2-containing gas. Examples of methods for contacting the alkaline aqueous solution with the CO2-containing gas include a method of spraying the alkaline aqueous solution and contacting it with the CO2-containing gas, a method of contacting the CO2-containing gas by bubbling it in the alkaline aqueous solution, and a method of contacting the alkaline aqueous solution with the CO2-containing gas so that they face each other.

[0023] When the alkaline aqueous solution contacts the CO2-containing gas, the CO2 in the gas reacts with the alkaline components in the alkaline aqueous solution to produce carbonates. Examples of carbonates include sodium bicarbonate, calcium carbonate, magnesium carbonate, and potassium carbonate. That is, the alkaline aqueous solution after contact with the CO2-containing gas may contain sodium bicarbonate, calcium carbonate, magnesium carbonate, and potassium carbonate. The liquid component (carbonate aqueous solution) after contact with the CO2-containing gas may further contain unreacted alkaline components (e.g., sodium hydroxide), components that do not react with CO2 (e.g., rare metal components such as scandium compounds and gallium compounds), and solid components that were not completely separated in the first solid-liquid separator 11. The amount of sodium bicarbonate in the carbonate aqueous solution may be 3% by mass or less, 2% by mass or less, or 1% by mass or less, based on the total mass of the carbonate aqueous solution.

[0024] The aqueous carbonate solution is transferred through transfer pipe L15 to a second solid-liquid separator 13. In the second solid-liquid separator 13, solid components that were not completely separated in the first solid-liquid separator 11 and poorly soluble carbonates (e.g., calcium carbonate) are separated from the aqueous carbonate solution. The second solid-liquid separator 13 may be, for example, a sedimentation concentration device such as a thickener.

[0025] The aqueous carbonate solution transferred through transfer pipe L16 contains water, sodium aluminum dioxide, sodium tetrahydroxide aluminate, sodium bicarbonate, magnesium carbonate, potassium carbonate, a scandium compound, a gallium compound, etc. The aqueous carbonate solution transferred through transfer pipe L16 has a composition, for example, of 0.5 mass % sodium aluminum dioxide, 2.5 mass % sodium tetrahydroxide aluminate, 1 mass % sodium bicarbonate, 0.1 mass % magnesium carbonate, 0.01 mass % potassium carbonate, 0.1 mass % scandium compound, 0.2 mass % gallium compound, and the remainder being water.

[0026] The solid components discharged through the transfer pipe L17 are a mixture containing calcium carbonate, iron oxide (Fe2O3), aluminum oxide, aluminum hydroxide, silicon oxide, titanium oxide, etc. These solid components may be separated into individual components and used as raw materials for cement, roads, building materials, etc., or may be disposed of by landfill.

[0027] The aqueous carbonate solution transferred through the transfer pipe L16 is transferred to the membrane separation device 14. In the membrane separation device 14, water is removed from the aqueous carbonate solution, and the aqueous carbonate solution is concentrated. The removal of water from the aqueous carbonate solution is performed using, for example, a reverse osmosis membrane.

[0028] The aqueous carbonate solution transferred through transfer pipe L19 contains water, sodium aluminum dioxide, sodium tetrahydroxide aluminate, sodium bicarbonate, magnesium carbonate, potassium carbonate, a scandium compound, a gallium compound, etc. The aqueous carbonate solution transferred through transfer pipe L19 has a composition, for example, of 1 mass % sodium aluminum dioxide, 5 mass % sodium tetrahydroxide aluminate, 2 mass % sodium bicarbonate, 0.2 mass % magnesium carbonate, 0.02 mass % potassium carbonate, 0.2 mass % scandium compound, 0.4 mass % gallium compound, and the remainder being water.

[0029] The water removed by the membrane separation device 14 is transferred through the transfer pipe L18. The transferred water is reused, for example, for mixing with red mud in the first solid-liquid separation device 11.

[0030] The carbonate aqueous solution from which the water has been removed is transferred through transfer pipe L19 to rare metal recovery device 15. In rare metal recovery device 15, rare metal components (scandium compounds, gallium compounds, etc.) contained in the carbonate aqueous solution are removed from the carbonate aqueous solution. The rare metal components are recovered using, for example, ion exchange resins, chelating resins, adsorbents, etc.

[0031] The carbonate aqueous solution from which the rare metal components have been recovered is transferred to the storage tank 16 through the transfer pipe L20. The carbonate aqueous solution transferred through the transfer pipe L20 contains water, sodium aluminum dioxide, sodium tetrahydroxide aluminate, sodium bicarbonate, magnesium carbonate, potassium carbonate, etc. The carbonate aqueous solution transferred through the transfer pipe L20 (the carbonate aqueous solution stored in the storage tank 16) has a composition, for example, of 1 mass % sodium aluminum dioxide, 5 mass % sodium tetrahydroxide aluminate, 2 mass % sodium bicarbonate, 0.2 mass % magnesium carbonate, 0.02 mass % potassium carbonate, and the remainder water. The carbonate aqueous solution stored in the storage tank 16 may be separated into its individual components, purified, and then used as valuable resources, or released into the environment (e.g., dumped into the ocean).

[0032] [Variations] The bauxite waste treatment facility does not necessarily have to be equipped with a first solid-liquid separation device. When the bauxite waste treatment facility does not have a first solid-liquid separation device, the mixture of red mud and water (alkaline aqueous solution) is brought into contact with CO2 to obtain an aqueous carbonate solution, and then solid components in the red mud and poorly soluble carbonates are removed from the aqueous carbonate solution by solid-liquid separation.

[0033] The bauxite waste treatment facility does not need to be equipped with a second solid-liquid separation device. In particular, if the solid components can be sufficiently removed by the first solid-liquid separation device and the amount of hardly soluble carbonates produced is small, the bauxite waste treatment facility does not need to be equipped with a second solid-liquid separation device. If the bauxite waste treatment facility does not have a second solid-liquid separation device, the alkaline aqueous solution from which the alkaline components of the red mud have been extracted is brought into contact with a gas containing CO2 to obtain an aqueous carbonate solution, and then water is removed from the aqueous carbonate solution using a membrane separation device.

[0034] If the bauxite waste treatment facility does not recycle water, it does not need to be equipped with a membrane separation device. If the bauxite waste treatment facility does not have a membrane separation device, the carbonate aqueous solution discharged from the second solid-liquid separation device is transferred to the rare metal recovery device.

[0035] [Bauxite waste treatment method] A method for treating bauxite waste using the bauxite waste treatment facility 100 will now be described. That is, one embodiment of the present invention is a bauxite waste treatment method. The bauxite waste treatment method includes at least the following steps. For the bauxite waste treatment method, reference can be made to the description of the bauxite waste treatment facility described above. (a) A step of mixing red mud containing an alkaline component and a rare metal component with water to obtain an alkaline aqueous solution containing the alkaline component. (b) A step of contacting an alkaline aqueous solution with a gas containing CO2 to obtain an aqueous carbonate solution. (c) A process for recovering rare metal components from the carbonate aqueous solution.

[0036] The bauxite waste treatment method according to this embodiment differs from conventional bauxite waste treatment methods in that it involves mixing red mud with water. Therefore, there is no need to concentrate the red mud, as compared to conventional methods, and the energy efficiency is superior to conventional methods. Furthermore, by using a larger amount of alkaline aqueous solution than conventional methods, it is possible to increase the contact area with CO2-containing gas, thereby enabling efficient CO2 removal. Furthermore, because rare metals are recovered directly from the carbonate aqueous solution, there is no need to concentrate the carbonate aqueous solution, and the energy efficiency is superior.

[0037] <(a) Process> Step (a) is a step of mixing red mud containing an alkaline component and a rare metal component with water to obtain an alkaline aqueous solution containing the alkaline component. Step (a) may be performed before step (b) or at substantially the same time as step (b).

[0038] Examples of alkaline components contained in red mud include sodium hydroxide, calcium hydroxide, magnesium hydroxide, and potassium hydroxide. Examples of rare metal components contained in red mud include scandium compounds, gallium compounds, and vanadium compounds.

[0039] The mixing of the red mud and water can be carried out by a known method, for example, the mixing of the red mud and water may be carried out in a stirring device or a solid-liquid separator.

[0040] The mixture of red mud and water may be, for example, 200 parts by mass or more, 500 parts by mass or more, or 1000 parts by mass or more of water per 100 parts by mass of red mud.

[0041] The pH of the alkaline aqueous solution is greater than 7, and may be 9 or greater, 10 or greater, or 11 or greater.

[0042] The bauxite waste treatment method may further include a solid-liquid separation step for removing solid components derived from red mud between steps (a) and (b). By removing solid components from the alkaline aqueous solution before contacting the alkaline aqueous solution with the CO2-containing gas, it becomes possible to contact the alkaline aqueous solution with the CO2-containing gas using a packed tower, a plate tower, a spray, or the like. The bauxite waste treatment method does not necessarily include a concentration step for concentrating the alkaline aqueous solution before carrying out the solid-liquid separation step.

[0043] <(b) Process> Step (b) is a step of contacting an alkaline aqueous solution with a gas containing CO2 to obtain an aqueous carbonate solution. The CO2-containing gas may be atmospheric air or exhaust gas. The CO2 concentration in the gas may be, for example, 1000 ppm or less, 700 ppm or less, or 500 ppm or less, or 100 ppm or more, 200 ppm or more, or 300 ppm or more.

[0044] Examples of carbonates that are produced by contacting an alkaline aqueous solution with a gas containing CO2 include sodium bicarbonate, calcium carbonate, magnesium carbonate, and potassium carbonate.

[0045] The method for contacting the alkaline aqueous solution with the CO2-containing gas is not particularly limited, and a method that provides excellent contact efficiency between the alkaline aqueous solution and the CO2-containing gas is preferred. Examples of methods for contacting the alkaline aqueous solution with the CO2-containing gas include a method of spraying the alkaline aqueous solution and contacting it with the CO2-containing gas, a method of contacting it by bubbling the CO2-containing gas in the alkaline aqueous solution, and a method of contacting the alkaline aqueous solution with the CO2-containing gas in a counter-flow manner. That is, step (b) may include spraying the alkaline aqueous solution and contacting it with the CO2-containing gas, or may include contacting the alkaline aqueous solution with the gas by bubbling the CO2-containing gas in the alkaline aqueous solution, or may include contacting the alkaline aqueous solution with the CO2-containing gas in a counter-flow manner.

[0046] The bauxite waste treatment method may further include a solid-liquid separation step between steps (b) and (c) for removing at least one of solid components derived from the red mud and a portion of the carbonates. By removing the solid components from the alkaline aqueous solution before recovering the rare metal components from the carbonate aqueous solution, contamination of the rare metal recovery equipment (e.g., adhesion of solid components to the ion exchange resin) can be suppressed, and the recovery efficiency of the rare metal components can be improved.

[0047] Examples of solid components removed in the solid-liquid separation step include iron oxide (Fe2O3), aluminum oxide, aluminum hydroxide, silicon oxide, titanium oxide, etc. Examples of carbonates removed in the solid-liquid separation step include calcium carbonate, etc.

[0048] The bauxite waste treatment method may further include a membrane separation step between steps (b) and (c) for removing water from the carbonate aqueous solution. Prior to recovering rare metal components from the carbonate aqueous solution, the carbonate aqueous solution is concentrated by removing either the alkaline aqueous solution or water. This reduces the amount of carbonate aqueous solution processed in the rare metal recovery device, improving the efficiency of recovering rare metal components. The membrane separation step is carried out, for example, using a reverse osmosis membrane. The water removed by the reverse osmosis membrane may be reused as water to be mixed with red mud.

[0049] When the bauxite waste treatment method further comprises, between steps (b) and (c), a solid-liquid separation step for removing solid components derived from red mud and a portion of carbonates, and a membrane separation step for removing water from the aqueous carbonate solution, it is preferable to carry out the membrane separation step after the solid-liquid separation step. By carrying out the membrane separation step after the solid-liquid separation step, it is possible to suppress fouling of the membrane separation device (for example, adhesion of solid components to the reverse osmosis membrane), and improve the efficiency of water removal in the membrane separation step.

[0050] <(c) Process> Step (c) is a step of recovering rare metal components from the carbonate aqueous solution, using, for example, an ion exchange resin, a chelating resin, an adsorbent, or the like.

[0051] In the bauxite waste treatment method, after step (c), the carbonate aqueous solution from which the rare metal components have been recovered may be released into the environment. When the carbonate aqueous solution from which the rare metal components have been recovered is released into the environment, there is no need to increase the purity of the carbonate in the carbonate aqueous solution obtained in step (c), and therefore energy loss is reduced compared to when the purity of the carbonate is increased. When the carbonate aqueous solution from which the rare metal components have been recovered is released into the environment, the concentration of the rare metal components in the carbonate aqueous solution may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. When the carbonate aqueous solution from which the rare metal components have been recovered is released into the environment, the concentration of the alkaline component in the carbonate aqueous solution may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less. [Example]

[0052] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the following examples.

[0053] Red mud and water are mixed so that 100 parts by mass of red mud and 100 parts by mass of water are mixed to obtain a slurry. The slurry after mixing contains 3% by mass of sodium aluminum dioxide, 1% by mass of sodium hydroxide, 0.1% by mass of calcium hydroxide, 0.1% by mass of magnesium hydroxide, 0.01% by mass of potassium hydroxide, 0.1% by mass of a scandium compound, and 0.2% by mass of a gallium compound in the liquid component, and iron oxide (Fe2O3), aluminum hydroxide, titanium oxide, and silicon oxide as solid components. The slurry is then separated into liquid and solid components by sedimentation and concentration using a thickener.

[0054] The separated liquid component (alkaline aqueous solution) is transferred to a CO2 absorption tower and brought into head-on contact with air while spraying the alkaline aqueous solution. This causes the alkaline component in the alkaline aqueous solution to react with the CO2 in the air, producing carbonates. The aqueous solution after contact with air is a carbonate aqueous solution containing 0.5 mass% sodium aluminum dioxide, 2.5 mass% sodium tetrahydroxide aluminate, 1 mass% sodium bicarbonate, 0.1 mass% magnesium carbonate, 0.01 mass% potassium carbonate, 0.1 mass% scandium compound, 0.2 mass% gallium compound, and the remainder being water.

[0055] The carbonate aqueous solution is brought into contact with a reverse osmosis membrane to remove water from the carbonate aqueous solution and concentrate it. The concentrated carbonate aqueous solution contains 1 mass% sodium aluminum dioxide, 5 mass% sodium tetrahydroxide aluminate, 2 mass% sodium bicarbonate, 0.2 mass% magnesium carbonate, 0.02 mass% potassium carbonate, 0.2 mass% scandium compound, 0.4 mass% gallium compound, and the remainder is water. The water removed by the reverse osmosis membrane is reused as water to be mixed with red mud.

[0056] The concentrated carbonate aqueous solution is brought into contact with an ion exchange resin to recover rare metal components from the concentrated carbonate aqueous solution. The carbonate aqueous solution after recovery of the rare metal components contains 1 mass% sodium aluminum dioxide, 5 mass% sodium tetrahydroxide aluminate, 2 mass% sodium bicarbonate, 0.2 mass% magnesium carbonate, 0.02 mass% potassium carbonate, and the remainder is water. The carbonate aqueous solution after recovery of the rare metal components has sufficiently low concentrations of alkaline components and rare metal components that it can be released into the environment. [Explanation of symbols]

[0057] 11...first solid-liquid separation device, 12...CO2 absorption device, 13...second solid-liquid separation device, 14...membrane separation device, 15...rare metal recovery device, 16...storage tank, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20...transfer pipe, 100...bauxite waste treatment facility.

Claims

1. (a) mixing red mud containing an alkaline component and a rare metal component with water to obtain an alkaline aqueous solution containing the alkaline component; (b) the alkaline aqueous solution and CO ２ and a gas containing the compound to obtain an aqueous carbonate solution; (c) recovering the rare metal component from the carbonate aqueous solution; A method for treating bauxite waste, comprising:

2. 2. The method for treating bauxite waste according to claim 1, further comprising a solid-liquid separation step between the step (a) and the step (b) for removing solid components derived from the red mud.

3. 2. The method of claim 1, wherein the gas is atmospheric air.

4. 2. The method for treating bauxite waste according to claim 1, wherein step (b) comprises spraying the alkaline aqueous solution and contacting the alkaline aqueous solution with the gas.

5. 2. The method for treating bauxite waste according to claim 1, wherein step (b) comprises contacting the gas with the alkaline aqueous solution by bubbling the gas through the alkaline aqueous solution.

6. 2. The method for treating bauxite waste according to claim 1, further comprising a solid-liquid separation step between the step (b) and the step (c) for removing at least one of solid components derived from the red mud and a portion of the carbonates.

7. 2. The method for treating bauxite waste according to claim 1, further comprising a membrane separation step between steps (b) and (c) for removing water from the aqueous carbonate solution.

8. 2. The method for treating bauxite waste according to claim 1, further comprising, after step (c), a step of releasing the aqueous carbonate solution from which the rare metal components have been recovered into the environment.

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